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Chapter 25
True mean draft
In previous chapters it has been shown that a ship trims about the centre of ¯otation. It will now be shown that, for this reason, a ship's true mean draft is measured at the centre of ¯otation and may not be equal to the average of the drafts forward and aft. It only does when LCF is at average e .
Consider the ship shown in Figure 25.1(a) which is ¯oating on an even keel and whose centre of ¯otation is FY aft of amidships. The true mean draft is KY, which is also equal to ZF, the draft at the centre of ¯otation.
e
Fig. 25.1(a)
Now let a weight be shifted aft within the ship so that she trims about F as shown in Figure 25.1(b).
Fig. 25.1(b)
e
